BACKGROUND: In patients with intractable constipation who are poorly responsive to medical treatments, surgical treatments may be considered. However, how preoperative physiologic evaluations contribute to some information in making surgical decision is not established. The aim of this study was to evaluate the outcome of surgical treatment in patients with severe constipation who underwent preoperative functional study. METHODS: Preoperative functional evaluation included colon transit time test, defecography, scintigraphic gastric emptying time test, anorectal manometry and balloon expulsion test. Nine patients with a mean age of 48 years old were taken total colectomy with ileorectal anastomosis. Slow colonic transit was demonstrated in each case. All patients were available for follow-up, with median time of 35 (range; 10-55) months. RESULTS: Seven patients (78%) were satisfied with outcome, improved the quality of life, and felt the operation was valuable despite of residual symptoms. Two patients did not experience symptom improvements. Six of seven colonic inertia or combined spastic pelvic floor syndrome patients had a satisfactory outcome. In contrast, one of two patients with generalized intestinal dysmotility did not show any improvement after surgery. CONCLUSIONS: Preoperative physiologic testing reliably identified patients with severe constipation who might have benefits from surgery. If cases are carefully diagnosed and selected, the surgical treatment may be highly effective in alleviating symptoms.